San Diego Zoo Veterinarian Meg Sutherland-Smith points to ultrasound video of a giant panda fetus. The ultrasound machine and a thermal camera helped the Zoo's giant panda team confirm that Bai Yun is pregnant for the fifth time since she arrived in San Diego in 1996. (SD Zoo photo)

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San Diego Zoo Veterinarian Meg Sutherland-Smith points to ultrasound video of a giant panda fetus. The ultrasound machine and a thermal camera helped the Zoo's giant panda team confirm that Bai Yun is pregnant for the fifth time since she arrived in San Diego in 1996. (SD Zoo photo)

She's not showing, but officials say ultrasound tests Monday showed a panda fetus and there may be a twin – although the second fetus probably will be reabsorbed before birth.

Zoo veterinarian Meg Sutherland-Smith says Bai Yun is due next month. Her offspring will weigh just 4 ounces. Bai Yun and the cub will remain in a den for four to five months but the zoo plans to show them on its live Panda Cam.

The father is zoo panda Gao Gao (Gow-Gow). The two mated in April.

Two of Bai Yun's cubs are at the zoo and two are in a breeding program in China.